This is something I've seen in a lot of newer games: How competent are the characters? Especially at the beginning?

I'm not certain how a new game designer would represent this in the book. For example, when I'm teaching a new game to experienced players, I can tell them "Your starting characters are about on par with 3rd level D&D Characters" or "Your starfighter pilot is about as competent as Luke in Empire Strikes Back."

But I'm not sure all games get that across. Especially with assorted mechanics.

The problem with not knowing can lead to players acting either too heroically or being too timid. I have been in games where the players took one look at the chance of success and walked away from an encounter. (This happened in TORG where the players realized that they had, at best, a 40% chance of swimming in calm water. When a little girl's father fell overboard into Shark Infested Turbulent Water, they looked at the girl and told her, "Tough luck" and walked away. Actually, after our first fight, we spent the rest of the adventure avoiding any and all conflict. There's a topic about difficulty but that's for another thread.)

Or games where the players don't realize that a single orc or skeleton is a deadly threat. An orc in Fate or Dungeon World is a different threat then an orc in D&D 2e.

For a character to feel "professionally competent" as in someone that relies on a skill for their livelihood, I consider that to be around 70% successful before opposition or defenses. That's my own benchmark after playing in a percentile system for 20+ years. It's where I like to start out a new character in their specialty.

If the phrase "professionally competent" doesn't mean anything to the reader, that's not going to convey much.